This paper discusses the problem of characterizing the level of geographic detail in digital form. That said, the traditional representative fraction seems useful but has many problems. Among these problems, I think assessing the fitness of data sets for particular use is most critical in practice. The authors argue that it is necessary to identify metric of level of geographic detail, but there is no perfect one can handle all the issues raised by the “legacy problem”. For example, for analyzing big data, traditional methods may be replaced by scale-free methods for segmentation. The evolving rate of technologies is much faster than 20 years ago, so the “legacy problem” will be more severe and frequent. Therefore, another requirement for the metric is sustainability. The metric itself should be readily updated to adapt to the new geographic environment.
For moving away from paper maps, having correspondent metaphors to the proposed metric is necessary, but it is harder than constructing the metric. To satisfy the requirements of being understood by a user lacking knowledge of conventions, the metaphors should be strictly straightforward. However, there is no rule for guiding the design of new metaphors. Following the traditions usually more efficient in practice although it will inherit the limits from paper maps. Metaphors for digital geographic world cannot be separated from its metric, but complete novel metaphors are not acceptable at this moment. In the transition from paper maps to digital maps, we always need to make a trade-off. Perhaps, when transition is completed, there are new technologies we need to adapt to. We will be always in the transition.